Rods for flame-spraying



March 2, 1965 W. M. WHEILDON, JR, ETAL RODS FOR FLAME-SPRAYING Filed April 6, 1961 INVENTORS,

WILL/AM MAXWELL WHEILDON J E- ELMEE G HUED ATTORNEY United States Patent 3,171,774 RQDS FOR FLAME-SPRAYENG William Maxwell Wheildon, In, Framingharn Center,

and Elmer G. Hard, Holden, Mass, assignors to Norton Company, Worcester, Mass, a corporation of Massachusetts Filed Apr. 6, 1961, der. No. 1%,699 9 Ciaims. (til. 161-177) This invention relates to improvements in rods for coating articles by flame-spraying and, in particular, flame-spraying of refractory material, and has for its principal objects to increase the rate of coating by providing a rod which may be subjected to rapid heating and feeding through a ceramic rod flame spray gun without spalling, fracturing, spitting, and the like, and hence without sacrifice in the uniformity of the surface; to provide a rod which is adapted to spraying by means of a ceramic rod flame spray gun without blow-back; and to provide a rod which can be manufactured expeditiously and economically.

This is accomplished herein by providing the rod with a fluted cross-section, that is, with a plurality of peripherally spaced, longitudinally disposed grooves in its surface. More specifically, the rods are made of bonded particles of refractory material and, in particular, zirconia and alumina, and have a relatively coarse grain skeletal-like structure.

The invention will now be described in greater detail with reference to the accompanying drawings wherein:

FIG. 1 is a perspective view of a rod drawn to about three times its actual size, showing flutes lengthwise thereof; and

FIG. 2 is a diametrical section taken on the line 22 of FIG. 1.

A method of flame-spraying of refractory materials is described in the Wheiidon patent, No. 2,707,691, wherein a relatively dense rod of solid cross-section comprised of relatively fine grain refractory metal is exposed to high temperature fusing and atomization in a spray gun, however, the rate of feeding and hence the rate of coating by this method is limited by the thermal shock conditions in the rod, induced by heating it with the high temperature flame, which if not properly accommodated may cause fracturing, spalling, and the like.

Ault, in his Patents 2,876,121 and 2,882,174, reduced the eliect of thermal shock by increasing the porosity of the rod by controlling grain size of the refractory material of which the rod is made, thus providing a rod of skeletal-like structure having considerably more porosity than rods theretofore known.

According to this invention, the rate of feeding and application of the desired coating of refractory materials according to Wheildon and Ault, can be materially increased without encountering spalling, fracturing, and the like of the rod, and hence without sacrifice in the uniformity of the coated surface, by increasing the surface area of contact of the rod with the fusing and atomizing flame. This is effected by changing the geometry of the cross-section of the rod to wit, by tinting the exterior surface of the rod.

Referring to FIGS. 1 and 2, the fluting preferably takes the form of a plurality of grooves it) formed in the surface peripherally of the rod which flutes extend length- Wise thereof. The grooves 10 may be uniformly spaced around the periphery of the rod and are shown as being substantially trapezoidal in cross-section. The rods are preferably formed by extrusion and for practical purposes the grooves should be of uniform depth in crosssection throughout the entire length of the rod to minimize the possibility of blow-back during operation of the gun.

3,?l,774 Patented Mar. 2, 1965 Zirconia rods in the order of and inch in diameter containing grooves in the order of of an inch in depth perform satisfactorily without spitting or fracturing.

By way of comparison, on the one hand, a inch solid zirconia rod manufactured as taught in the Ault patent, can be sprayed at a maximum rate of 5 inches per minute without undue spalling and hence provide a satisfactory coating. On the other hand, an eight-fluted zirconia rod of the same composition and maximum diameter, but with a volume per linear inch of approximately 21% less than the solid rod can be sprayed at the maximum rate of 11 to 14 inches per minute. This gives overall lay down of coating or a spraying rate for the fluted rod which is twice that of the conventional solid cylindrical rod.

The flutes herein shown are truncated; however, the shape may be varied to suit the character of the spray gun and its nozzle and there may be a greater or lesser number of flutes.

The zirconia and alumina rods referred to above are preferably made according to the specification outlined in the Ault patents; however, this is not intended to be exclusive of rods made according to the Wheildon specification, or any or all of the compositions disclosed therein, or according to any other known methods of rod fabrication, for the reason that the improved fluted geometry of the rod improves the rate of spraying and hence the rate of coating regardless of the character or origin of the particles with which the rod may be made.

Hence it is considered to be within the scope of this invention to make fluted rods of relatively dense construction by extruding and firing a mixture of relatively fine grain of any of the oxides enumerated in the Wheildon patent, and to expect a marked improvement in the rate of feed due to the fluted geometry of the rods. Prefcrabiy, however, the rods are made of coarser grain so as to have a skeletal-like structure as disclosed in the Ault Patents 2,876,121 and 2,882,174.

Thus, it is contemplated that fluted zirconia rods may be made by mixing coarse grain zirconium oxide particles with a temporary binder, extruding the mixture to form a fluted rod of suitable dimensions, and firing the rod to sinter the particles and drive off the binder. Preferably the zirconia particles are selected from the group consisting predominantly of cubic and tetragonal crystals. Rods made of such particles have a porosity of from 8% to 40% of open and interconnecting pores and a modulus of rupture of more than 2000 pounds per square inch. By using a proper firing cycle and a particle size gradation in which at least 30% by weight is coarser than 100 microns and substantially all are finer than 500 microns, a porosity may be obtained in which more than of the pores are in excess of 20 microns in diameter. Such rods are about 96% pure zirconia, are much less susceptible to thermal shock and hence to splitting and spitting than the denser rods, and accordingly full advantage can be taken of the fluted construction disclosed herein to increase the rate of feed and hence the rate of coating. Correspondingly, the rods may be made of sintered aluminum oxide as disclosed in the Ault patent, No. 2,882,174, The firing cycle and particle size is chosen so that the resulting rod has a porosity of from about 8% to 40% of open and interconnecting pores, a modulus of rupture of about 2000 pounds per square inch, contains at least by weight of aluminum oxide, and in which more than 50% of the pores are in excess of 20 microns in diameter. For the best results, at least 30% by weight of the particles should be coarser than 100 microns, with substantially all of them finer than 500 microns. Fused aluminum oxide or calcined aluminum oxide, or a mixture of these may be employed.

According to the preferred practice, the refractory particles for making the rods are obtained by crushing furnace cast pigs of fused ore to size. Particles obtained in this fashion are crystalline and substantially anhydrous.

The source of the refractory particles is not important so long as they can be obtained in suflicient purity and as long as the size is maintained substantially in the order of magnitude proposed in the Ault patents. The particles may be crystalline, flake-like, amorphous, or mixtures thereof.

It should be understood that the present disclosure is for the purpose of illustration only and that this invention includes all modifications and equivalents which fall within the scope of the appended claims.

We claim:

1. For coating articles by flame-spraying, a rod consisting essentially of bonded particles of refractory material, said rod having a cross-section showing a fluted periphery.

2. For coating articles by flame-spraying, a rod consisting essentially of bonded particles of refractory material, said rod having circumferentially disposed, longitudinally extending grooves.

3. For coating articles by flame-spraying, a rod consisting essentially of bonded particles of refractory material, said rod having circumferentially disposed,-lngitudinally extending, substantially trapezoidal-shaped grooves.

4. For coating articles by flame-spraying, a rod consisting essentially of bonded particles of refractory material, said rod having an outer diameter in the order of at least about of an inch, a plurality of grooves in its peripheral surface disposed lengthwise thereof, and

said grooves having a depth in the order of 1[3g of an inch.

5. For coating articles by flame-spraying, a rod consisting essentially of bonded particles of refractory material, said rod having an outer diameter in the order of at least about of an inch, and having eight peripherally disposed grooves extending lengthwise thereof in the order of of an inch in depth.

6. For coating articles by flame-spraying, a rod consisting essentially of bonded particles of zirconia, said rod having a cross-section showing a fluted periphery.

7. For coating articles by flame-spraying, a rod consisting essentially of bonded particles of alumina, said rod having a cross-section showing a fluted periphery.

.8. For coating articles by flame-spraying, a rod consisting essentially of sintered zirconia crystals, said rod having a porosity of 8% to 40% open and interconnect ing pores, containing at least 96% of pure zirconia, and being characterized in that it has a cross-section showing a fluted periphery.

9. For coating articles by flame-spraying, a rod consisting essentially of sintered alumina crystals, said rod having a porosity of 8% to 40% open and interconnecting pores, containing at least pure alumina, and being characterized in that it has a cross-section showing a fluted periphery.

Ault Mar. 3, 1959 Ault Apr. 14, 1959 

1. FOR COATING ARTICLES BY FLAME-SPRAYING, A ROD CONSISTING ESSENTIALLY OF BONDED PARTICLES OF REFRACTORY MATERIAL, SAID ROD HAVING A CROSS-SECTION SHOWING A FLUTED PERIPHERY. 